A conventional Stable Approach Monitor (SAM) operates to reduce landing risks and runway excursions by providing one or more audible advisories developed around a set of stable approach criteria. Generally, the stable approach criteria are developed around the Standard Operating Procedure (SOP) used by most major airlines and criteria developed by the Flight Safety Foundation. By way of example, the stable approach criteria may include altitude gates (i.e., height above runway) in which the “stability” of the aircraft is determined. In addition, the stable approach criteria provides that at these altitude gates, the aircraft must be properly configured to land, for example flaps at least partially deployed and the landing gear down. The aircraft must be on a proper glide slope and be traveling at or near a predetermined speed. In one sense, the stable approach criteria may determine a “stability envelope” such that if the aircraft is outside that envelope upon passing a selected altitude gate then the SAM will provide an audible advisory. Further, the stability envelope may be tailored, within certain limits, to meet additional or stricter requirements of individual airline SOPs. Ideally, the SAM should not provide nuisance advisories and thus should not be heard during normal operation of the aircraft.
By way of example, one type of SAM may provide an audible advisory such as “GEAR-GEAR” if the landing gear is not configured to land at a predetermined altitude. The SAM may provide an audible advisory such as “FLAPS-FLAPS” if the trailing edge flaps are not set at a predetermined flap detent at the predetermined altitude. Between a range of altitudes, for example between 950 feet and 450 feet above the runway, the SAM may provide an audible advisory such as “TOO HIGH, TOO HIGH” or “TOO FAST, TOO FAST.” At 450 feet, if the pilots have not properly reacted to the one or more advisories, the SAM may announce “UNSTABLE, UNSTABLE,” which operates as an instruction to the pilot to abort the landing and perform a go-around.
As noted, present SAMs provide a “FLAPS-FLAPS” advisory when the trailing edge flaps are not appropriately set as the aircraft descends below a predetermined altitude above the runway. Trailing edge flaps are deployed to increase the aspect ratio of the wing and to provide additional lift for the aircraft. The trailing edge flaps are generally moved through a number of different settings, detents or positions as the aircraft slows to its predetermined approach speed. The flap placard speeds indicate the maximum allowable for each flap detent. The purpose of the SAM advisory regarding flap deployment is to inform the pilot to deploy the trailing edge flaps in accordance with the stable approach criteria. One drawback of the existing SAM is when the aircraft speed is too high on final approach for landing flaps to have not been set. In this final approach scenario, the existing SAM provides an audible advisory to deploy the flaps based on the aircraft being at the predetermined height above the runway and independent of aircraft speed. If the pilot were to heed the advisory and deploy the flaps, there is a potential for structural damage to the flaps and the potential that a post-flight inspection of the flap system will be required.